The invention relates to a plasma processing apparatus that processes a substrate-like sample, such as a semiconductor wafer, which is used during a process of manufacturing a semiconductor device and is placed on a sample stage disposed in a processing chamber inside a vacuum container, using plasma formed in the processing chamber, and particularly to a plasma processing apparatus that processes a sample placed on a sample stage while keeping an in-plane temperature of the sample at a desired value.
Along with the trend of miniaturization of semiconductor devices, the accuracy required for an etching process, which is necessary to manufacture the semiconductor devices, becomes strict year by year. In order to deal with such a problem, it is important to control a surface temperature of a sample within a range of a desired value during etching in a plasma processing apparatus that performs an etching process on a semiconductor wafer using plasma inside a vacuum container.
In recent years, the etching process is performed in a plurality of steps in the state of holding one sample on a sample stage in response to a request for further improvement of shape accuracy. There is a demand for a technique of controlling a surface temperature distribution of the sample to be optimum for each step condition during the process.
In general, an upper surface of a sample stage provided in a plasma processing apparatus has an electrostatic chuck structure. That is, a configuration in which electric power is supplied to an electrode, disposed inside a film-shaped dielectric material constituting an upper surface of the sample stage, to adsorb and hold a wafer placed on the film by static electricity is provided, and further, a heat transfer medium such as a He gas is supplied between a back surface of the wafer and a film surface to promote heat transfer between the wafer and the sample stage even in vacuum.
Further, a cooling means using a refrigerant flow path through which a heat transfer medium (refrigerant) such as water and a coolant flows and a heating means such as a heater are disposed inside a member disposed inside the sample stage in order to control a temperature of a placement surface of the sample stage on which the wafer is placed within a desired range. The temperatures of the placement surface of the sample stage and the wafer are controlled by increasing or decreasing a heat exhaust amount by the cooling means and a heating amount by the heating means. For example, in a typical plasma etching processing apparatus, a temperature of a wafer is controlled to a value within a range suitable for processing by controlling an output of a heater while allowing a refrigerant whose temperature has been controlled to a value within a predetermined range by a refrigerant temperature control device such as a chiller device to flow in a refrigerant flow path inside a sample stage.
The wafer being plasma-processed is heated by ion incidence or the like from plasma. In addition, the wafer is heated by receiving heat from an upper surface of the sample stage on which the wafer has been placed even when the heating means such as the heater is disposed inside the sample stage. At this time, it is desirable that a distribution of magnitude of heat transfer inside the sample stage be one desired by a user in terms of controlling a temperature value and a distribution thereof to values within a desired range with respect to an in-plane direction of the wafer. However, in practice, the distribution of magnitude of heat transfer tends to be non-uniform in the in-plane direction by being affected by the influence of an internal structure such as a shape of the refrigerant flow path disposed inside the sample stage, and such influence of the structure becomes an impediment factor in controlling the wafer temperature to the value suitable for processing.
More specifically, when a flow path that allows a refrigerant to flow therethrough is disposed inside a metallic base material disposed inside a cylindrical sample stage, it is physically difficult to dispose the flow path so as to have uniform positions in a radial or peripheral direction over the entire in-plane direction of an upper surface of a circular or substantially circular shape of the sample stage.
This is because not only the refrigerant flow path but also parts and structures disposed for other purposes, for example, cables and connectors for supplying power to adsorb the substrate-like sample to be processed such as the semiconductor wafer placed on the upper surface by static electricity and power to cause the heater to generate heat, cables or connectors for supplying radio-frequency power of a predetermined frequency supplied to an electrode disposed in a dielectric film constituting the base material or the upper surface on which the sample is placed, a passage for supplying a gas having heat transferability such as He, which is supplied to a gap between the upper surface of the sample stage and the sample placed and adsorbed onto the sample stage, a through-hole in which a plurality of pins that moves the sample upward or downward, the sample in the state of being placed at a distal end of the pin and supported above the upper surface of the sample stage, is disposed and vertically moves, and the like are disposed inside the sample stage including the base material, and when preferable positions for disposing these parts and a preferable position for disposing the refrigerant flow path overlap each other, one or both of them are disposed at a location deviating from the preferable position so as to satisfy specifications required by the user such as a customer in consideration of the performance of sample processing.
Conventionally, such a trade-off in terms of design has always been selected in determining a structure of a device to be manufactured. In a general plasma processing apparatus, a portion where a refrigerant flow path is non-uniformly disposed in the radial direction or the peripheral direction is generated in the in-plane direction of the upper surface of the sample stage. Representative examples of the portion of the refrigerant flow path disposed in the vicinity thereof include an inlet and an outlet of the refrigerant. In regions inside and the upper surface of the base material in the vicinity of such portions, a heat exchange amount caused by the refrigerant (the amount of heat exhaust in case of cooling the sample) tends to become non-uniform in the radial or peripheral direction.
Conventionally, a technique disclosed in JP 2003-60019 A is known as a technique for solving such a problem. This conventional technique discloses a wafer stage on which a semiconductor wafer is mounted and which includes: a base material having a refrigerant flow path for allowing a refrigerant for temperature adjustment to flow; a stress-reducing member provided on a wafer setting side of the base material and having a smaller thermal expansion coefficient than the base material; a dielectric film provided on the wafer setting side of the stress-reducing member; and a deflection-preventing member provided on a wafer non-setting side of the base material and having a smaller thermal expansion coefficient than the base material.
In this conventional technique, breakage of the dielectric film due to a difference in linear expansion coefficient between the base material and the dielectric film is suppressed by disposing the stress-reducing member between the base material and the dielectric film. Titanium as a material of the stress-reducing member, aluminum as the base material, and titanium as the deflection-preventing member are disclosed.
In addition, JP 2010-21405 A discloses a vacuum processing apparatus having a lift pin housed inside a through-hole disposed on a sample stage to raise and lower an object to be processed. The vacuum processing apparatus is configured such that an outer peripheral edge of a portion on a tray at a distal end of the lift pin is brought into close contact with the periphery of the through-hole on an upper surface of the sample stage during processing of the object to be processed to hermetically close the through-hole so that it is possible to prevent heat conduction between a space inside the through-hole and the object to be processed above the through-hole from becoming singularity locally different from other portions and to obtain heat transfer with small variations over the entire upper surface of the sample stage.